1. Field
The present invention relates to optical communication modulation and detection methods, apparatuses and systems. The present invention also relates to optical modulation and detection methods in coherent optical transmission systems.
2. Related Art
Over the last decade, there has been continued research in the field of optical communication systems to improve receiver sensitivity. Particular emphasis has been placed upon free-space optical communications. Moreover, research has been conducted in increasing receiver sensitivity and/or reducing the required signal photons per bit (ppb) in order to improve transmission link performance.
Generally, optical transmission links transmit both optical polarizations with equal attenuation. For example, in free-space optical links, the signal-carrying light is conveyed from the transmitter to the receiver via a free-space medium. Telescopes at both ends of the links collimate and collect light before and after propagation. If the link is bi-directional and polarization isolation is needed to suppress cross-talk, the transmitter and/or receiver telescopes may be configured to pass only one polarization. In such instances, modulation formats requiring both optical polarizations simply will not work as expected. That is, the data carrying capacity as well as the sensitivity of the receiver will significantly be reduced.
Data transfer rates in telecommunication systems are currently at about 100 Gb/s per wavelength. While dual polarization modulation formats exhibit good capacity, other modulation schemes are being researched and developed to obtain good receiver sensitivity and capacity in a commercial capacity in the telecommunications field.
What is desired in the art is an optical link configured to support a single polarization.
What is also desired in the art is an optical link that employs less hardware while maintaining current standards of sensitivity.
What is further desired in the art is an optical link that employs less hardware while maintaining current standards of capacity.
What is yet even further desired in the art is an optical link that exhibits improved sensitivity.
What is yet even further desired in the art is an optical link that can operate on a single polarization and maintain nearly the sensitivity of an optical link employing a modulation format requiring both optical polarizations.